Half-Life fans, here is some bad news. In a recent interview with SevenDayCoolDown, Gabe revealed that Valve's silence is fairer to the Half Life fans. According to Gabe, Valve has not finalised the formula yet and they are still experimenting with Half Life 3's concept. As Gabe said:
The problem is, we think that the twists and turns that we're going through would probably drive people more crazy than just being silent about it, until we can be very crisp about what's happening next.
In addition, in an email exchange with a forum member at Valve Time, Valve's Gabe Newell revealed that Valve would not announce anything new in this year's E3. So there you have it guys :-P